This invention relates to a composition having a hard metal surface formed by metal spraying, wherein the back side is reinforced by fiber-reinforced plastics and so on, a method for producing thereof, and a mold release agent used in the producing method. The composition is intended for works of art or ornaments such as a relief or a statue which presents a metallic appearance, or flooring materials which requires abrasion resistance, or a mold for molding resin.
The fiber-reinforced plastics (referred to as FRP hereinafter) being light and strong, and having superior heat resistance and weather resistance have been widely accepted in a field where metal materials were used previously. However, the surface of FRP is not so hard in comparison with that of metals or the like. Consequently, if the FRP is used for purposes requiring high surface durability, for example, flooring materials, a mold for molding a resin, or the like, the FRP is inclined to become not suitable because of its surface cracks or abrasion. Therefore, improvement of such a defect has been desired.
Also, in the field of works of art, it has been adapted that the surface of an article comprising FRP or non-fibrous resin is metal-sprayed to form a metal layer providing a metallic appearance. In this case, however, the polishing process is needed to render the roughly sprayed surface smooth and shiny. Therefore, when a finely rugged pattern is required on the metal surface, an additional process such as machining by hand engraving or the like after the polishing is essential, which takes a lot of time and technique. Here, in this specification, "a (finely) rugged pattern" means a pattern made by (fine) unevenness.
In order to overcome the above noted problem, various procedures have been devised heretofore. One known arrangement, for example Japanese Official Patent Provisional Publication, Showa 60-121022 discloses that the surface of an original mold made of wood or gypsum is coated with a mold release agent comprising such as PVA resin. After that, the mold is sprayed with such metals as Zn or Zn-Al alloy being comparatively soft and having a low melting point. The back side of the sprayed metal layer is reinforced by a reinforcing layer comprising FRP or the like. Thus obtained composition consisting of the sprayed metal layer and the reinforcing layer is released from the original mold. Thus, the pattern of the surface on the original mold is transferred onto the surface of the sprayed metal layer on the composition. The above procedure makes it possible precisely to transfer the finely rugged pattern of the original mold onto the surface of the sprayed metal layer and to increase the surface hardness which has been a defect of the FRP.
However, the above Zn or the like which has been commonly used for metal spraying is suitable for transfer of the original mold surface pattern by means of metal spraying, but not hard enough to maintain abrasion resistance. Therefore, they are undesirable when used for various uses such as a mold which requires mechanical strength and other characteristics. Then, metals such as nickel, the stainless steels or the like which have superior characteristics have been desired to be used as a metal for spraying.
However, there is a problem that nickel or the stainless steel having a high melting point does not adhere to the surface of the mold even if these metals are sprayed. Also, there is a defect that the finely rugged pattern formed on the original mold cannot be precisely transferred and that the reproduction of the rugged pattern is bad.
Various methods have been devised heretofore to produce a superior composition comprising a sprayed metal layer and the FRP by means of above transfer process utilizing the high melting point metals such as nickel or the stainless steels.
For example, it is known that if minute uneveness is formed on the original mold surface by the blast processing or the like, adhesion of the high melting point sprayed metal layer is improved.
Japanese Official Patent Gazette, showa 61-61891 discloses the following procedure. At first, a mold is made of wood or gypsum. Then an inversion mold of said mold is formed with heat resisting resin such as silicone rubber. Utilizing the inversion mold, a secondary mold having the same shape as that of the original is made by precisely casting antimony or the like which is not apt to expand and has low melting point. After positioning pins made of high melting point metal on the surface of the secondary mold, high melting point metal is sprayed and the back side thereof is reinforced with silica sand. After removing the pins and secondary mold by using melting fusion process, the inversed surface pattern of the original mold is obtained on the surface of the high melting point sprayed metal layer. In this case, the pins placed in the secondary mold of low melting point metal improve adhesion of high melting point metal.
Japanese Official Patent Gazette, showa 63-6327 discloses that after applying a surface treatment to a mold made of a material to be easily processed such as wood, plastics or the like by using a surface treatment agent containing water-soluble adhesive such as water glass or the like and red iron oxide as main components, then nickel or chromium is sprayed by cold metal spraying. Here, in this specification, "cold metal spraying" means a method wherein the mold temperature does not become high even if a hot metal melted under high temperature is sprayed on the mold. On the metal layer formed by this cold metal spraying, the surface pattern of the original mold is transferred. The surface treatment agent makes it easy to release the metal layer from the mold, and the cold metal spraying enables use of a non-heatproof mold.
Japanese Official Patent Gazette, heisei 2-23331 discloses that the silicone elastomer containing a fireproof filling agent such as quartz is used as surface materials of the mold. The fireproof filling agent is used to prevent damage caused by the heat during metal spraying.
The Japanese Official Patent Gazette, heisei 2-54422 discloses that in case of spraying a metal directly on the product substrate, the product substrate previously coated with resin containing minute particles is metal sprayed to improve adhesion of the sprayed layer.
However, above mentioned prior art procedures are not sufficient to improve adhesion of the high melting point sprayed metal securely and to reproduce the surface pattern of the original mold.
For example, in the method comprising forming a minute unevenness uniformly on the entire surface of the original mold by blast processing etc., in case that there is a finely rugged pattern on the original mold, this finely rugged pattern is erased and the finely rugged pattern cannot be transferred on the surface of the high melting point sprayed metal layer. Therefore, in this case, a further processing by hand engraving or etching is required to make the rugged pattern on the surface of the high melting point sprayed metal layer obtained. As a result, labor and cost for processing are consumed. Also, in such an additional processing, it is impossible to reproduce the very same finely rugged pattern as that of the original mold, and scattering of finished quality is large. Furthermore, if the blast processing is carried out, it is impossible to finish the high melting point sprayed metal layer surface into the specular one. Therefore, in case of necessity of a specular surface for the product surface, it is required to carry out an additional processing for making a specular surface by means of grinding etc.
The procedure cited in Japanese Official Patent Gazette, showa 61-61891 requires removal of the pins and elimination of the pin traces by means of grinding. Therefore, the finely rugged pattern cannot exist around the setting place of the pin. Grinding of the pin trace may eliminate also the original pattern. At the position distant from the pin setting places, adhesion cannot be improved. This procedure requires the aforementioned blast treatment and cause the same problem stated above. Also in this procedure, the secondary mold formed by precise casting of antimony or the like is sprayed with high melting point metal. The precise casting requires the extremely high technology and a long term treatment. Furthermore, in order precisely to cast the secondary mold, additional processes and time are required to make an inversed mold of heatproof material such as silicone rubber in accordance with the original mold of gypsum.
According to the procedure cited in Japanese Official Patent Gazette, showa 63-6327, the cold metal spraying method is adopted because of using the material such as wood or gypsum which are readily processed but not heatproof. In the cold metal spraying method, the surface of the high melting point sprayed metal layer formed becomes roughly uneven like that of the ground glass. Therefore, even if a finely rugged pattern is formed on the original surface, the finely rugged pattern cannot be transferred on the high melting point sprayed metal layer. The above prior art provides that metal being readily processed and having a low melting point may be utilized as the original mold. However, such an original mold has the same problem stated above as for Japanese Official Patent Gazette, showa 61-61891 concerning time and cost.
Regarding the procedure cited in Japanese Official Patent Gazette, heisei 2-23331, high melting point metal layer cannot be finely formed because mold characteristics and mechanical strength of silicone elastomer to be sprayed with the high melting point metal is inferior to that of metal mold or the like. Therefore, it is desirable to make the elastomer surface rough or to spray the low melting point metal such as Zn/Al alloy thinly on the elastomer surface in order to improve adhesion of the high melting point sprayed metal layer. However, if the silicone elastomer surface is made to be rough, a finely rugged pattern disappears. When the low melting point metal is sprayed on the surface of the silicone elastomer, the surface of the low melting point metal becomes irregularly uneven, so that the original mold's finely rugged pattern is buried and disappears. Also, if the high melting point metal is sprayed directly on the surface of the low melting point sprayed metal layer, when the high melting point metal layer is mold-released from the silicone elastomer surface, the sprayed layer of the low melting point metal remains adhering to the surface of the high melting point sprayed metal layer, so that a product having the high melting point sprayed metal layer on the surface cannot be obtained.
The procedure provided in Japanese Official Patent Gazette, heisei 2-54422 improves adhesion of a sprayed metal layer to the substrate, but it is difficult to release the sprayed metal layer from the substrate. Therefore, it is not adoptable for transferring the original mold surface pattern to the sprayed metal layer by releasing the sprayed metal layer from the original mold after the sprayed metal layer is formed on the original mold surface.